This Work, undertaken at His Lordship's request, is inscribed as a testimony of the Author's esteem and regard. Although it has unavoidably exceeded the limits of the Publications of the Society for the Diffusion of Useful Knowledge, for which it was originally intended, his Lordship still thinks it may tend to promote the views of the Society in its present form. To concur with that Society in the diffusion of useful knowledge, would be the highest ambition of the Author,
MARY SOMERVILLE.